High density connector and method of manufacture

ABSTRACT

Electrical connectors capable of being mounted on circuit substrates by BGA techniques are disclosed. Also, disclosed is a method of manufacturing such connectors. There is at least one recess on the exterior side of the connector elements. A conductive contact extends from adjacent the interior side into the recess on the exterior side of the housing. A controlled volume of solder paste is introduced into the recess. A fusible conductive element, in the form of solder balls is positioned in the recess. The connector is subjected to a reflow process to fuse the solder ball to the portions of the contact extending into said recess. Contacts are secured in the insulative housing of the connector by deformable sections that minimize stress imposed on the central portions of the contacts to promote uniformity of solder volume.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to electrical connectors and moreparticularly high I/O density connectors, such as array connectors.

2. Brief Description of Prior Developments

The drive to reduce the size of electronic equipment, particularlypersonal portable devices, and to add additional functions to suchequipment, has resulted in an ongoing drive for miniaturization of allcomponents, especially electrical connectors. Efforts to miniaturizeconnectors have included reducing the pitch between terminals in singleor double row linear connectors, so that a relatively high number of I/Oor other lines can be interconnected by connectors that fit withintightly circumscribed areas on the circuit substrates allotted forreceiving connectors. The drive for miniaturization has also beenaccompanied by a shift in preference to surface mount techniques (SMT)for mounting components on circuit boards. The confluence of theincreasing use of SMT and the required fine pitch of linear connectorshas resulted in approaching the limits of SMT for high volume, low costoperations. Reducing the pitch of the terminals increases the risk ofbridging adjacent solder pads or terminals during reflow of the solderpaste. To satisfy the need for increased I/O density, array connectorshave been proposed. Such connectors have a two dimensional array ofterminals mounted on an insulative substrate and can provide improveddensity. However, these connectors present certain difficulties withrespect to attachment to the circuit substrates by SMT techniquesbecause the surface mount tails of most, if not all, of the terminalsmust be beneath the connector body. As a result, the mounting techniquesused must be highly reliable because it is difficult to visually inspectthe solder connections or repair them, if faulty. In the mounting of anintegrated circuit (IC) on a plastic or ceramic substrate the use ofball grid array (BGA) and other similar packages has become common. In aBGA package, spherical solder balls attached to the IC package arepositioned on electrical contact pads of a circuit substrate to which alayer of solder paste has been applied, typically by use of a screen ormask. The unit is then heated to a temperature at which the solder pasteand at least a portion or all of the solder ball melt and fuse to anunderlying conductive pad formed on the circuit substrate. The IC isthereby connected to the substrate without need of external leads on theIC.

While the use of BGA and similar systems in connecting an IC to asubstrate has many advantages, a corresponding means for mounting anelectrical connector or similar component on a printed wiring board(PWB) or other substrate has yet to be developed. It is important formost situations that the substrate-engaging surfaces of the solder ballsare coplanar to form a substantially flat mounting interface, so that inthe final application the balls will reflow and solder evenly to aplanar printed circuit board substrate. Any significant differences insolder coplanarity on a given substrate can cause poor solderingperformance when the connector is reflowed onto a printed circuit board.To achieve high soldering reliability, users specify very tightcoplanarity requirements, usually on the order of 0.004 inches.Coplanarity of the solder bails is influenced by the size of the solderball and its positioning on the connector. The final size of the ball isdependent on the total volume of solder initially available in both thesolder paste and the solder balls. In applying solder balls to aconnector contact, this consideration presents particular challengesbecause variations in the volume of the connector contact receivedwithin the solder mass affect the potential variability of the size ofthe solder mass and therefore the coplanarity of the solder balls on theconnector along the mounting interface.

Another problem presented in soldering connectors to a substrate is thatconnectors often have insulative housings which have relatively complexshapes, for example, ones having numerous cavities. Residual stresses insuch thermoplastic housings can result from the molding process, fromthe build up of stress as a result of contact insertion or a combinationof both. These housings may become warped or twisted either initially orupon heating to temperatures necessary in SMT processes, such astemperatures necessary to reflow the solder balls. Such warping ortwisting of the housing can cause a dimensional mismatch between theconnector assembly and the PWB, resulting in unreliable solderingbecause the surface mounting elements, such as solder balls, are notsufficiently in contact with the solder paste or close to the PWB priorto soldering.

A need, therefore, exists for reliably and efficiently mounting highdensity electrical connectors on substrates by surface mountingtechniques.

SUMMARY OF THE INVENTION

Electrical connectors according to the present invention provide highI/O density and reliable attachment to circuit substrates by SMTtechniques. These connectors exhibit high coplanarity along the mountinginterface.

Electrical connectors of the present invention are ones in which one ormore terminals are connectable by a fusible electrically conductivematerial to a substrate. This fusible electrically conductive materialis a solder mass, preferably comprising a solder ball that can bereflowed to provide the primary electrical current path between theterminal and a circuit substrate.

An aspect of the invention includes methods for forming an exteriorfusible conductive contact on an element of an electrical connector.According to one method, a recess is formed on the exterior side of theconnector elements or contacts. A section of a conductive contactextends from adjacent the interior side of the conductor element intothe recess on the exterior side of the housing. The recess is filledwith a controlled volume of solder paste. A fusible conductive element,for example a solder ball, is positioned in the recess on the exteriorside of the housing. The conductive element placed in the recess is thenheated to a temperature sufficient to fuse the solder paste and fuse thefusible conductive element to the section of the contact extending intosaid recess.

Also encompassed by this invention is a contact for use in an electricalconnector which comprises a terminal tab area where said contact isconnectable to a fusible conductive element, such as a solder ball. Amedial area of the contact is positioned between the terminal tab and acontact area. The medial area is adapted to resist molten solder flow,for example, by application of a coating or plating of a non-solderwettable material. By this arrangement wicking of the solder from thesolder ball from the area of attachment to the contact avoided.

Coplanarity of the surface mounting interface of the connector ismaintained by providing an insulative connector housing in which stressbuildup is avoided. According to this aspect of the invention, a contactterminal is inserted into an opening in the housing. The cross sectionof the opening is configured so that at least one side thereof has orcomprises a shaped projection adapted to be deformed by the terminals asthe terminal is inserted into the opening. By means of this arrangement,stress build up as a result of multiple contact insertions is avoided,so as to minimize warping and twisting of the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

The method and connector of the present invention is further describedwith reference to the accompanying drawings in which:

FIG. 1 is a top plan view of a receptacle connector of a preferredembodiment of the connector of the present invention;

FIG. 2 is a partially cut away end view of the receptacle shown in FIG.1;

FIG. 3 is a top plan view of a plug element of a preferred embodiment ofthe present invention;

FIG. 4 is a partially cut away end view of the plug element shown inFIG. 3;

FIG. 5 is a cut away end view of the receptacle and plug shown in FIGS.1-4 in unmated relation;

FIG. 6 is an end view of the receptacle and plug shown in FIG. 5 inmated relation;

FIGS. 7 a, 7 b and 7 c are cut away end views showing respectivelyfirst, second and third sequential stages in the mating of thereceptacle end plug shown in FIG. 5;

FIG. 8 is a bottom plan view of the receptacle shown in FIG. 1 beforethe placement of solder balls thereon;

FIG. 9 is a bottom plan view of the receptacle shown in FIG. 8 afterplacement of the solder balls thereon;

FIG. 10 is a detailed cut away view of area XII in FIG. 1;

FIG. 11 is an enlarged view of the cut away area in FIG. 4;

FIG. 12 is an enlarged view of the cut away area in FIG. 10;

FIG. 13 is an enlarged cross sectional view through 13-13 in FIG. 10;

FIG. 14 is a top plan view of a second preferred embodiment of areceptacle connector of the present invention;

FIG. 15 is an end view of the receptacle shown in FIG. 14;

FIG. 16 is a top plan view of a second preferred embodiment of a plugconnector of the present invention;

FIG. 17 is an end view of the plug shown in FIG. 16;

FIG. 18 is an end-view of the mated receptacle and plug shown in FIGS.14-17;

FIG. 19 is a top plan view of a receptacle used in a third preferredembodiment of a receptacle connector of the present invention;

FIG. 20 is an end view of the receptacle shown in FIG. 14;

FIG. 21 is a top plan view of the plug element of the third preferredembodiment of a plug connector of the present invention;

FIG. 22 is an end view of the plug element shown in FIG. 2;

FIG. 23 is an end view of the mated receptacle and plug shown in FIGS.19-22;

FIG. 24 is a side cross sectional view in fragment of another embodimentof a connector according to the present invention;

FIG. 24 a is a fragmentary view of a portion of the structure of FIG. 24modified to form a deeper recess;

FIG. 25 is a front cross sectional view in fragment of the connectorshown in FIG. 24 in which the plug and receptacle are unmated;

FIGS. 26 a and 26 b is a graph showing temperature versus time anddistance during solder reflow in Examples 1 and 2 of the method of thepresent invention;

FIGS. 27 a-27 f are laser generated profiles of the product of Example 3of the method of the present invention;

FIGS. 28 a and 28 b are x-ray photographs showing the product of Example4 of the method of the present invention;

FIGS. 28 c and 28 d are electron microscope photographs showing theproduct of Example 4 of the method of the present invention.

FIG. 29 is a view similar to FIG. 10 in which the ground and powercontacts have been omitted;

FIG. 30 is a cross sectional view through XXXI-XXXI in FIG. 13;

FIG. 31 is a computer generated representation of predicted stresses inan insulative housing similar to those illustrated in the preferredembodiments of the present invention;

FIG. 32 is a graph of contact retention force as a function of theamount of deformation (compression) in a rib of the insulative housingas is shown in FIG. 29;

FIG. 33 is a front elevational view of a receptacle signal contact usedin a preferred embodiment of the connector of the present invention;

FIG. 34 is a front elevational view of a plug signal contact used in apreferred embodiment of the connector of the present invention;

FIG. 35 is a front elevational view of a receptacle ground/power contactwith carrier strip used in a preferred embodiment of the connector ofthe present invention; and

FIG. 36 is a front elevational view of a plug ground/power contact withcarrier strip used in a preferred embodiment of the connector of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring generally to FIGS. 1-2 and 12-13, a set of intermatingconnectors according to a first embodiment of a high density connectorof the present invention includes a receptacle which is shown generallyat numeral 10. A base section of the receptacle is shown generally atnumeral 12. The base is preferably formed by molding an appropriateinsulating polymeric material capable of withstanding SMT reflowtemperatures, for example, liquid crystal polymer (LCP). Referring firstto the base section, this element includes a base wall 14 having anexterior side 16 and an interior side 18. On the exterior side there areouter recesses as, for example, recesses 20, 22, 24, 26 and 28 (FIG.12). On the interior side there are inner contact receiving recesses as,for example, recesses 30, 32, 34, 36 and 38. Connecting these inner andouter recesses are medial slots as, for example, slots 40, 42, 44, 46and 48. Each of the outer recesses has a base wall and a lateral wallas, for example, base wall 50 and lateral wall 52 (FIG. 12). Each of theinner signal contact receiving recesses has a base wall and intersectinglateral walls as, for example, base wall 54 and lateral walls 56 and 58.Each of the inner ground or power contact receiving recesses also has abase wall and diagonal lateral walls as, for example, base wall 60 andlateral walls 62 and 64. The above described inner and outer recessesand connecting medial slots receive ground/power contacts or signalcontacts.

The ground or power contacts preferably have an upper section, showngenerally at numeral 66, formed of two contacting forks 68 and 70. Eachof these forks has a converging section 72, a contact point 74 and anoutwardly diverging or lead-in section 76. The ground or power contactsalso include a medial section 78 passing through the lower wall of thereceptacle and a lower section 80 that extends into the outer recess. Asolder ball 82 is fused onto lower section 80, as will be describedbelow.

Each of the signal contacts (FIGS. 12 and 13) includes an upper sectionshown generally at numeral 84 preferably having a contact projection 86,a lead-in bend 88 and a stiffening rib 90. The signal contacts alsoinclude a medial section 92 which passes through the lower wall of thereceptacle. Each signal contact includes a lower section 98 (FIG. 13)extending into the outer recess for example, recess 22 in FIGS. 12-13,where a solder ball 100 is fused to lower section 98 as will beexplained below.

Referring particularly to FIGS. 1-2, the base section of the receptacleincludes latching structures, for example, as is shown generally atnumeral 102. This latching structure includes an upward tab 104 which issuperimposed over a vertical groove 106 and which has an outwardprojection 108. The base section of the receptacle also has othersimilar latching structures 110, 112 and 114. The receptacle alsoincludes an upper section shown generally at 116 which is superimposedover the base section. This upper section has a top wall 118 and aperipheral side wall 120. This upper section is fixed to the basesection by means of latching structures as is, for example, showngenerally at numeral 122. Each of these latching structures has a sidewall recess 124 and a U-shaped latch 126 which extends downwardly fromthe top wall and is spaced from the side wall recess. The tab 104 fitsbetween the U-shaped latch 126 and the side wall recess 124 to enablethe U-shaped latch to engage the outward projection 108 on the latchingstructure 102 of the base section. The upper section includes othersimilar latching structures 128, 130 and 132 which engage, respectively,latching structures 110, 112 and 114 on the base section. The uppersection 116 or the base 102 also may have mounting brackets 134 and 136which have fastener apertures 138 and 140, respectively. On the top wall118 of the upper section 116 there are also signal contact accessapertures as, for example, apertures 142 and 144. These access aperturesare arranged in a plurality of rows corresponding to the rows of signalcontacts in the base section. Interposed between these rows of signalcontact access apertures are elongated ground or power contact accessslots as, for example, slots 146 and 148. The upper section 116 forms amating interface between receptacle 10 and a mating plug 150 describedbelow.

Referring to FIGS. 3-4 and FIG. 11, the plug element of the connector isshown generally at numeral 150. The plug includes a base wall 152 and aperipheral side wall 154. There are opposed gaps 156 and 158 in the sidewall and there is an open side 160 in opposed relation to the base wall.Projecting laterally from the plug are mounting brackets 162 and 164having fastener receiving apertures 166 and 168 respectively, that arealignable with the fastener receiving apertures 138, 140 in the mountingbrackets of the receptacle.

Referring to FIG. 11, on the inner side of the base wall 152 there areinner signal contact receiving recesses such as recess 170. Also on theinner side of the base wall are inner power or ground contact receivingrecesses such as recess 172. In opposed relation to the outer recesseson the base wall there are outer signal contact receiving recesses suchas recess 174, and outer power or ground contact receiving recesses, asat recess 176. Connecting the outer and inner signal contact receivingrecesses and the outer and inner power or ground contact receivingrecesses are, respectively, medial slots 178 and 180. Mounted in thepower/ground contact receiving recesses via the medial slots 180 arepower or ground contacts, shown generally at numeral 182. Each contact182 has an elongated inner section 184, an elongated medial section 186,which is mounted in base wall 152, and an outer section 188 extendinginto recess 176. A solder ball 190 is fused onto section 188. The outersection 188 and the solder ball are partially contained in the outerrecess 176. The plug also includes a plurality of signal contacts 192.These signal contacts each have an inner section 194, a medial section196 mounted in the base wall, and a terminal tab 198 extending intorecess 174. A solder ball 200 is fused onto terminal tab 198. Again itwill be observed that this outer section and the solder ball arepartially contained in the outer recess as at 170.

Referring to FIGS. 5-7 c, it will be seen that the plug described aboveis mounted on a circuit substrate, such as a rigid PWB 202, and thereceptacle is mounted on a similar PWB 204. The plug and receptaclethereby form a board to board interconnection, as illustrated in FIG. 6.The plug has a two dimensional array of signal contacts, such as 192onto which are fused solder balls 200 and a plurality of ground/powercontacts, such as contacts 192, onto which are fused solder balls 190.By use of SMT techniques, the solder balls are also fused to the PWB 202to fix the entire plug to the PWB and effect electrical contact betweenthe signal contacts and ground or power contacts in the plug and thePWB. It will be appreciated that although not all contacts areillustrated in FIG. 5, all such contacts are connected to solder ballsand to the PWB in the same way. Similarly, solder balls 100 are fusedonto receptacle signal contacts 84 and those solder balls are fused tothe PWB 204. Receptacle ground/power contacts 66 are mounted in slot 134and are fused to solder balls 82 and these solder balls are fused to PWB204.

The plug is aligned with the receptacle so that the peripheral side wall154 of the plug overlaps the peripheral side wall 120 of the uppersection 118 of the receptacle.

Referring particularly to FIGS. 7 a-7 c the engagement of the plug andreceptacle is shown in greater detail. FIG. 7 a shows, after initialalignment, the ground/power contacts in the plug initially entering theground/power contact receiving slots in the receptacle and engaging thecorresponding power/ground contacts in the receptacle. The signalcontacts have entered the signal contact slots in the receptacle. FIG. 7b shows the signal contacts in the plug initially engaging thecorresponding signal contacts in the receptacle and the power/groundcontacts in the plug becoming further engaged between the opposed leavesof the power ground contacts in the receptacle. FIG. 7 c shows that thesignal contacts in the plug being fully engaged with the signal contactsin the receptacle. The power/ground contacts in the plug have becomepositioned at the base of the fork of the power/ground contacts in thereceptacle.

Referring to FIG. 8, the exterior side 16 of the base section 12 of thereceptacle is shown prior to the application of the solder balls. Priorto the application of the solder balls, the terminal tabs of the signalcontacts, for example, terminal tab 82, and of the power groundcontacts, for example terminal tab 98, are disposed within acorresponding outer recesses for example, outer recesses 20, 22, 24, 26and 28, by insertion of the contacts into the opposite surface 18 of thebase 12. A quantity of solder paste of appropriate composition isapplied to substantially fill each outer recess. The solder balls arethen applied over the outer or mounting surface of the base. Preferably,the outer recesses are smaller in transverse extent than the solderballs, so that the solder balls are supported on the edges of therecesses, at a position near the terminal tabs of the contacts. Tomaximize the stability of the solder ball in the recess, a recess thatis round or the shape of a regular polygon in cross-section ispreferred. The solder paste aids in holding a solder ball in each of theexposed recesses as is shown in FIG. 9, where, for example, solder ball82 is shown in recess 20 and solder ball 100 is shown in recess 22.Additional solder balls, 230, 232 and 234 are shown, for example, inrecesses 24, 26 and 28. A solder ball will be positioned in all of theouter recesses of the receptacle. It will also be understood that theexterior side of plug will be substantially identical to the exteriorside of the receptacle before placement of the solder balls as is shownin FIG. 8 and after emplacement of the solder balls as is shown in FIG.11. After emplacement of the solder balls in the outer recesses, theconnector is subjected to a reflow process to fuse the solder bails ontothe terminal tabs. The exterior sides of the connectors, together withthe solder balls and particularly the outer surfaces of the solderballs, form a substantially planar mounting interface, along which theconnector is mounted onto a supporting circuit substrate, such as a PWB.

FIGS. 10 and 13 show a variant of the FIG. 1 embodiment wherein, insteadof the forked receptacle contacts 66, oppositely disposed pairs 66 a and66 b of blade type contacts engage the ground/power terminals 182.

FIGS. 14-18 illustrate a second preferred embodiment of a set ofintermating connectors of this invention. Referring particularly toFIGS. 14-15, this set includes a receptacle shown generally at numeral236. This receptacle includes an insulative housing shown generally at238 which has an inner side 240, a lateral side 242 and an exterior side244. The housing also includes opposed alignment projections 246 and248. On the inner side of the housing there are contacts 250 and 252each having sections which bow away from each other and then converge toa contact point from which then again diverge. Contacts 251 are mountedon base 231 in the same manner as the embodiments shown in FIGS. 1-13.Solder balls, such as solder ball 254, are mounted to the board side ofcontacts 250 and 252 in the same manner as described above. Referringparticularly to FIGS. 16 and 17, the set also includes a plug showngenerally at 258 which includes an insulative housing shown generally at260 having an inner side 262, a peripheral lateral side 264 and anexterior side 266. At one end of the housing there are a pair ofvertical end walls 268 and 270 with a medial end recess 272. At theopposed end of the housing there are another pair of end walls 274 and276 with a medial end recess 278. Extending from the inner side of thehousing there are a plurality of contacts as at contact 280 that extendfrom recesses as at 282. Onto each of these contacts is fused a solderball 284. It will also be seen that these contacts are positioned in astaggered arrangement. For example, contact 286 is offset with respectto contact 280, so rows of contacts can be spaced closer together toincrease contact density. Referring particularly to FIG. 18, it will beseen that each contact in the plug such as contact 280 is verticallyaligned with one of the pairs of converging contacts, such as contacts250 and 252, in the receptacle and is interposed between theseconverging contacts. It will also be seen that the alignment projections246 and 248 also engage the end recesses 272 and 278 in the plug. Inthis embodiment the separate ground/power contacts used in the FIGS.1-13 embodiment are not present. Such functions can, if desired, beincorporated into the undivided contacts pairs.

FIGS. 19-23 show a third preferred embodiment of a set of intermatingconnectors. The plug is shown generally at numeral 290. This plugincludes a housing generally 292 having a base wall 294 and a peripherallateral wall 296, as well as opposed alignment projections 298 and 300.The base wall of the housing has an inner side 302 and an outer side304. Signal contacts, such as contact 306, extend from inner side 302.It will be seen that the signal contacts are also staggered or offset inalternate rows, to increase contact density. The plug also includesground or power contacts 310, 312, 314 and 316 arranged adjacent each ofthe sides of the plug parallel to one side of the lateral wall. On theexterior side of the base wall are signal contact solder balls, such assolder ball 318, and power ground contact solder balls, such as 320,which are fused to their respective contacts in the same way asdescribed with respect to the first embodiment. The receptacle is showngenerally at numeral 322 and has an insulative housing 324 that includesa base wall 326, a peripheral lateral wall 328 and alignment projectionreceiving recesses 330 and 332. The base wall also has an exterior side334 and an inner side 336. Projecting from the inner side are signalcontacts such as contacts 338 and 340. The contacts in adjacenttransverse rows are also axially offset to allow an increase in contactdensity. Parallel to each side of the peripheral wall there are lateralpower or ground contacts 342, 344, 346 and 350. On the exterior side ofthe base wall there are for each signal contact a solder ball, such assolder ball 352. There are also solder balls, such as at solder ball354, for attaching each of the power or ground pins. Referring toparticularly to FIG. 23, it will be seen that at the plug 290 engagesreceptacle 322.

As previously mentioned, components such as electrical connectors, thatare to be mounted on circuit substrates by SMT techniques must-meet verydemanding specifications for coplanarity. If tight tolerances oncoplanarity, usually on the order of about 0.003 to about 0.004 inch,are not maintained, manufacturers experience undesirably high failurerates resulting from faulty solder connections. Variations in thedistance of a surface mount portion of a contact from the circuitsubstrate can result from variations in the location of the contact inthe insulative housing occurring as a result of the contact insertionprocess and from deformation of the housings, resulting in bowing orwarping of the mounting interface of the connector body. Connectors madein accordance with the present invention are capable of attaining strictcoplanarity requirements by use of features that carefully locate andsize the fusible bodies used for bonding the connector to a substrateand by the use of contact securing arrangements that preventaccumulations of stresses in the connector housing that tend to distortthe housing.

In the embodiments of FIGS. 1-23 the metal contacts are secured ininsulative housings in a manner to avoid the inducing of stress in thebody of the housing. This securing is achieved by the use of a shapedslot or opening into which a securing portion of the contact isinserted. In one arrangement especially useful for the smaller signalcontacts, the slot has a shape that closely conforms in shape anddimensions to all the surfaces of the contact but one. The wall of theslot facing that one surface has an integrally molded lateral projectionprojecting into the slot. The distance between the distal end of theprojection and the opposing wall of the slot is less than the thicknessof the contact. Thus the distal portion of the projection is engaged byand deformed by the contact as it is inserted into the slot. The contactis held securely in the slot by the normal force exerted on the contactby the deformable projection. Because the distal of the projection isfree to deform, the build up of stresses in the housing is avoided. Inthe preferred embodiments illustrated, the projection comprises apyramidal rib integrally formed on one of the side walls of the slot.

The specific rib configuration illustrated is believed to be optimum forthe particular housings in which it is employed, but other similar ribsof somewhat different shape or size might be advantageously employedwith other types of housings. Referring particularly to FIGS. 29 and 30,a signal contact 494 is retained in slot 496 and abuts against rib 498.The rib has a planar surface 500, where it engages the contact 494, andopposed oblique sides 502 and 504. The contact 494 is securely retainedin the slot by engagement with the back and side edges of the slot 496and rib 498. The portion of the rib adjacent surface 500 is free todeform as contact 494 is forced into slot 496, thereby relieving anystresses that result from contact insertion.

Similarly, a power/ground contact is retained in slot 508 and bearsagainst deformable rib 510. The rib has a distal portion 512, where itabuts against the contact, and opposed oblique sides 514 and 516. Inthis arrangement, there is also an opposed rib as, for example, rib 518.This opposed insulative rib also has a distal portion 520 and obliquesides 522 and 524. The opposed deformable ribs can be used for securinglarger contacts and for centering the contact in the slot. Those skilledin the art will also appreciate the particular shape, size, number andplacement of such ribs may vary for different types of housings; andthese factors would be selected so that, to the greatest extentpossible, stresses in the housing are isolated in the deformable ribs.FIG. 31 which was generated using ANSYS stress analysis softwareavailable from Ansys, Inc. of Houston, Pa. shows that by use of thecontact securing arrangement illustrated in FIGS. 29 and 30, high levelsof stress are essentially isolated in the ribs, and do not extendsubstantially beyond the contact mounting slots thereby significantlyreducing the risk of warpage or twisting of the housing which couldotherwise result from a large number of contact insertions. The unitsfor the various stress areas shown in FIG. 31 is N/mm² and the mm is theunit for displacement shown. FIG. 32 shows that, for a typical contact494, increases in deformation (compression) of the distal portion of thedeformable rib up to about 0.0004 inch resulted in an increasingretention force between the contact and the housing, resulting from thenormal force imparted on the contact by the rib. After 0.0004 inches ofdeformation (compression), only minor increases in retention forceresulted.

As previously mentioned, another factor influencing coplanarity of thesubstrate mounting face of a connector utilizing BOA mounting is theuniformity of the size of the solder balls and the position of thesolder balls with respect to the board mounting face of the connectorhousing. In the preferred embodiments previously described, thetermination tab of each contact is positioned in a recess. The outerrecesses are substantially uniform in size and shape. These recessesprovide several features of importance with respect to the presentinvention. The recesses can receive a highly uniform amount of solderpaste placed therein, for example, by a simple deposit and squeegeeoperation. Thus the amount of solder available for securing each solderball onto a contact is substantially uniform. The recesses locate theposition of each solder ball in the lateral X-Y directions prior toattachment of the solder balls onto the contacts. The recesses alsolocate the solder balls in the Z direction with respect to the bottomsurface of the housing and the distance of the solder ball from theterminal tabs of the contacts. The nominal extension of the tab into therecess is set so that at the maximum of the tolerance for extension ofthe tab into the recess, the tab does not touch the solder ball andthereby influence its Z direction location. However, fusing of thesolder ball onto the contact tab is assured by having a relativelyuniform and adequate amount of solder, from the solder paste, in therecess. Any variation in the distance between the contact tab and thesolder ball is absorbed by the variable volume of solder paste placed inthe recess.

In order to maintain an adequate amount of solder adjacent the solderball during the reflow step used to attach the solder balls onto thecontacts and to prevent solder wicking onto the engagement surfaces ofthe contact, the contact is treated to resist solder wicking. Referringparticularly to FIG. 33, contacts 526 and 528 are shown attached to acarrier strip 530. The contacts have a contact engagement area 532usually plated with non-oxidizing metals such as gold, palladium oralloys of palladium. The contacts also have a central area 534, aportion of which forms the contact retention area in the housing. Ananti-solder wicking or non-solder wettable material is applied to thecentral area 532. One preferred material for this purpose is nickelplating. While not intending to be bound by any particular theory, it isbelieved that the solder resistant feature of this nickel plated arearesults from or is enhanced by the oxidation of the nickel afterplating, for example, by exposure to ambient air for several days.Surprisingly and unexpectedly, it is found that the nickel or nickeloxide barrier prevents or reduces solder wicking in such contacts. Forthe nickel or nickel oxide plating to have such a passivation function,it is preferred that the plating have a thickness of from 10 μin to 100μin and more preferably about 50 mm. Other solder wick resistantmaterials are believed to be usable for this purpose, such as flourinecontaining solder resist coatings. These may be especially useful if theentire contact is plated with a continuous outer layer of a solderwettable metal, for example, gold. The contact tab area 536 maypreferably be plated with a solder receptive material such as gold, tinor tin alloys. Preferably the entire contact will be plated with nickel.On the upper section there is a precious metal layer selectively platedover the nickel. This upper section precious metal plating willpreferable have a thickness of from 10 μin to 100 μin and morepreferable 30 μin. On the lower section there is a solder wettable metallayer selectively plated on the lower section. Alternatively, anelectroplated layer of chromium can be substituted for the nickel layer.Referring to FIG. 34, plug signal contacts 538 and 540 are shownattached to a carrier strip 542. Each of these contacts has a goldplated tab area 544, a nickel plated central retention and anti-wickingarea 536 and a precious metal plated engagement area 548. Similarly inFIG. 35, the ground/power contact 550 is shown attached to carrier strip552. This contact has a lower gold plated tab area 554, a nickel platedcentral anti-wicking area 556 and an upper gold plated contactengagement area 558. Another feature of ground/power contact 550 whichis also found to reduce wicking is a series of notches in the tab area554 such as notches 560, 562 and 564. Another feature of ground/powercontact 550 which was included in embodiments disclosed above isvertical slots such as slot 566. Referring to FIG. 36, a plugground/power contact 568 is shown which has a lower gold plated tab area570, a nickel plated central anti-wicking area 572 and an upper goldplated area 574. It will be seen that ground/power contact 568 does nothave a separate carrier strip, but it does have apertures such asaperture 576 which allow the contact itself to serve this carrierfunction. With each of the contacts described above it will beunderstood that tin or other solder wettable material may be substitutedfor gold in the lower area. For all the contacts shown in FIGS. 33-36the width of the lower gold plated tab area as is, for example, shown atw₁ in FIG. 36 will preferably be from about 0.1 mm to about 0.25 mm. Thewidth of the nickel plated central area as is shown, for example, at w₂in FIG. 36 will preferably be from about 0.1 mm to about 1 mm.

Referring to FIGS. 24-25, an embodiment of the invention having anotherarrangement for affixing solder balls is shown. The receptacle of thisconnector is shown generally at numeral 324. This receptacle has a basewall 326 having an exterior side 328 and an interior side 330. On theexterior side there are recesses such as at recesses 332, 334, 336, 338,and 340, (FIG. 25) 342 and 344 (FIG. 24). Each of these recessespreferably has an oblique base wall 360 having a rounded surface 362. Onthe interior side 330 there are recesses as at recess 346, 348, 350,352, 354 (FIG. 25), 356 and 358 (FIG. 24). Between the exterior andinterior recesses there are medial slots as at slot 364, 366, 368, 370,372 (FIG. 25), 374 and 376 (FIG. 24). Each of these slots has aretention projection (not shown) for retaining the contact in the slot,in a manner substantially the same as that previously discussed inconnection with FIGS. 29 and 30. On the interior side, the receptaclehas substantially the same construction as the receptacle illustrated inFIGS. 1 and 2. It includes an upper section 436 secured on base 326 in asuitable manner, preferably by latches (not shown) as discussed withrespect to FIGS. 1 and 2. The upper section or cover 436 has a pluralityof openings, such as openings 452 and 460, for receiving individualcontacts from a mating plug or slots, such as slots 454, 456, 468 (FIG.25) for receiving ground or power contacts from the mating plug. Thesignal contacts, such as contact 408, and ground/power contacts are of aform substantially as described with respect to any of the previousdescribed embodiments. For example, the ground contact 382 (FIG. 25) hasa lower section 384 from which there is a tab 386. This contact also hasan upper section shown generally at numeral 388 which is made up offorks 390 and 392. Each of these forks has a converging section 394 andan outwardly diverging lead-in section 396. The tab 386 is located inrecess 336. Each signal contact, such as contact 408, has an uppersection 410 with a forward projection 412 and rearward bend 414. Thesignal contact also has a medial section 416 where it engages theinsulative housing and a lower tab 418 located in recess 334.

The tab 386 of ground contact 382 and the tab 418 of signal contact 408are formed by bending the tail portions of the respective terminalsabout the surfaces 362, after the contacts are inserted into base 326.Each surface 362 serves as bending mandrel for an associated contacttail. The tails are bent to the extent of the oblique surface 360 andare allowed to spring back so that the tabs are transverse to thelongitudinal axis of the contact and are substantially parallel to thesurface 328. This assures a high degree of coplanarity of the tabs.Subsequent to formation of the tabs, solder paste is applied to theoutside surface of each tab. Solder balls, such as 398, 400, 402, 404,406 (FIG. 25), 426 and 428 (FIG. 24) are then applied to the tabs andthe assembly is heated to fuse the solder paste and solder ball ontoeach tab. In an alternative structure, shown in FIG. 24 a, the recess334 a are deepened so that surfaces 360 a and 362 a are positionedfurther from bottom surface 328 a. As a result, the solder ball 398 a islocated partially within the recess 334 a and is stabilized by the edgesthereof, as previously discussed especially with respect to FIGS. 12 and13. As a result, when solder balls of highly uniform size are used,these arrangements can yield finished connectors that exhibitcoplanarity of the contacts across the mounting interface.

A plug having generally the same construction as the plugs previouslydescribed is shown generally at numeral 430. It includes a base wall 432having an exterior side 434 and an interior side 436. On the exteriorside there are recesses as at recess 438, 440, 442, 444 and 446. Each ofthese recesses has an oblique base wail 448 and a curved wall 450.Connecting with each of these recesses are contact slots 452, 454, 456,458 and 460. The plug also has a number of power/ground contacts as, forexample, is shown generally at numeral 462. Each of these contacts has acontact section 464 that engages the forks of the ground/power contactsof the receptacle. These contacts also have a medial section 466 whereit engages the housing and a solder ball tab 468 for receiving a solderball 470. The plug also includes a number of signal contacts as, forexample, is shown generally at numeral 476. Each of these signalcontacts includes a contact section 478 which engages the signalcontacts in the receptacle, a medial section 480 where it engages thehousing and a solder ball tab 482 for receiving a solder ball. Othersignal contacts as at 486 and 488 engage respectively other solder ballsas at 490 and 492. The solder ball tabs are formed and solder balls 470,474, 484, 490 and 492 are applied to the plug in substantially the samemanner as previously described with respect to the receptacle.

In the method of this invention the conductive element will preferablybe a solder ball. Those skilled in the art, however, will appreciatethat it may be possible to substitute other fusible materials which havea melting temperature less than the melting temperature of theinsulative body. The fusible element can also have a shape other than asphere. The solder ball or other conductive element will also preferablyhave a diameter which is from about 50 percent to 200 percent of thewidth of the recess. This diameter will also preferably be related tothe depth of the recess and be from 50 percent to 200 percent of thatdepth. The volume of the solder ball will preferably be from about 75percent to about 150 percent of the volume of the recess and, morepreferably, will be about the same volume as the recess. The contact tabwill extend into the recess by a sufficient amount to present adequatesurface area for the solder ball to fuse to, and will usually preferablyextend into the recess from about 25 percent to 75 percent and morepreferably to about 50 percent of the depth of the recess as previouslymentioned. The recesses ordinarily will be circular, square or the shapeof any other regular polygon in cross section. When the conductiveelement is solder, it will preferably be an alloy which is in the rangeof about 90% Sn and 10% Pb to about 55% Sn and 45% Pb. More preferablythe alloy will be eutectic which is 63% Sn and 37% Pb and has a meltingpoint of 183° C. Typically, a “hard” solder alloy with a higher leadcontent would be used for mating to materials such as ceramics. The“hard” solder ball will “mushroom” or deform slightly as it softensunder typical SMT conditions, but will not melt. A “soft” eutectic ballis used for attachment to PCB's and will usually reflow and reformitself under typical SMT conditions. Other solders known to be suitablefor electronic purposes are also believed to be acceptable for use inthis method. Such solders include, without limitation, electronicallyacceptable tin-antimony, tin-silver and lead-silver alloys and indium.Before the solder ball or other conductive element is positioned in arecess, that recess would usually be filled with solder paste.

Alternatively, in place of the solder ball previously described, a bodyof material which is not fusible at SMT temperatures may be attached byreflow of the solder paste in the recesses onto the contacts. Theconnector mounting interface would comprise a plurality of infusiblespheres in a tightly coplanar array. Such a connector would be securedon a substrate by conventional SMT techniques.

While it is believed that a solder paste or cream incorporating anyconventional organic or inorganic solder flux may be adapted for use inthis method, a no clean solder paste or cream is preferred. Such solderpastes or creams would include a solder-alloy in the form of a finepowder suspended in a suitable fluxing material. This powder willordinarily be an alloy and not a mixture of constituents. The ratio ofsolder to flux will ordinarily be high and in the range of 80%-95% byweight solder or approximately 80% by volume. A solder cream will beformed when the solder material is suspended in a rosin flux. Preferablythe rosin flux will be a white rosin or a low activity rosin flux,although for various purposes activated or superactivated rosins may beused. A solder paste will be formed when a solder alloy in the form of afine powder is suspended in an organic acid flux or an inorganic acidflux. Such organic acids may be selected from lactic, oleic, stearic,phthalic, citric or other similar acids. Such inorganic acids may beselected from hydrochloric, hydrofluoric and orthophosphoric acid. Creamor paste may be applied by brushing, screening, or extruding onto thesurface which may advantageously have been gradually preheated to ensuregood wetting. Although it has been found that wicking of the solder ontothe contact is significantly reduced when a solder paste or cream isused, it is believed that paste type solder flux alone may also be usedwhen a suitable, passivation agent is used. Such a suitable passivationagents would include fluoride containing solder resist coatings such asFLOURAD which is available from the 3M Corporation.

Heating is preferably conducted in a panel infra red (IR) solder reflowconveyor oven. The solder element would ordinarily be heated to atemperature from about 183° to about 195° C. but, depending on thematerial of the housing, solders having melting temperatures may beused. The conveyor oven would preferably be operated at a rate of speedfrom about 10 to 14 inches per second and would be moved through aplurality of successive heating phases for a total time of about 5minutes to about 10 minutes. Prior to being inserted into the conveyoroven the connector housing, contacts and solder elements may bepreheated at an elevated temperature for at least an hour. In theconveyor oven a temperature profile would be developed based on anappropriate peak temperature, maximum slope and time above reflowtemperature. Peak temperature is the highest temperature reached by thehousing. For a solder element with a melting point of 183° C., peaktemperature would usually be between 185° C. and 195° C. Maximum slopeis measured in ° C./sec. and specifies how fast the connector housingtemperature is allowed to change, so as to avoid warping or bending. Formost applications of this method, maximum positive slope will preferablyinitially be from about 2° C./sec to 15° C./sec. After the wetting pointof the solder is reached negative slope will preferably be −2° C./sec to−15° C./sec. An important aspect of the method of this invention is thattime above reflow is minimized, Time above reflow is a measure of howlong the solder element remains in its liquid phase. It is found thatwhen time of the solder in its liquid phase is minimized, wicking ofsolder from the recess up the contact is eliminated or significantlyreduced. Preferably rise time of temperature as measured on the boardbetween 180° C. and 200° C. and fall time of temperature as measured onthe board between 200° C. and 180° C. will both be from about 10 secondsto about 100 seconds. While not intending to be bound by any particulartheory, it is believed that during such relatively short periods oftime, surface tension of the liquid solder element will restrain theliquid solder from flowing through the contact receiving slot in thebase of the recess. After such periods of time, however, the liquidsolder will begin to flow through the contact receiving slot and wick upthe contact. Prior to bringing the temperature of the solder element toits melting temperature, it may also be advantageous to initially have arelatively high slope but before melting temperature is reached to slowthe rate of temperature increase or decrease after which a relativelyhigh slope is then adopted until the melting temperature is reached. Theselection of an appropriate housing material may also: enhance results.Preferably the housing material will be wholly aromatic liquid crystalpolyester (LCP) with characteristics of high glass transitiontemperature, low thermal coefficient, low moisture absorption, highfracture toughness, good flow and low viscosity, high temperature andhigh flash point.

The method of the present invention is further described with referenceto the following examples.

Example 1

An insulative housing for a connector plug and receptacle substantiallyis described above in connection with FIGS. 1-18 was made. Contacts alsosubstantially in accordance with that description were also positionedin the housing. These contacts were beryllium copper and were platedwith gold over their entire surface area to a thickness of 30 microns.The housing material was DUPONT H6130 liquid crystal polymer (LCP). Thelength and width of the plug were respectively 52.5 mm (includingmounting brackets) and 42.36 mm. The recesses on the exterior surfacesof the plug and receptacle housing were cross sectionally square havinga side dimension of 0.62 mm and a depth of 0.4 mm. About 2 mm of thecontact extended into the recess. Other dimensions were generally inproportion to the above dimensions in accordance with FIGS. 1-18. On theexterior sides of both the plug and receptacle the recesses were filledor substantially filled with CLEANLINE LR 725 no clean solder creamwhich is commercially available from Alphametals, Inc. of Jersey City,N.J. Both the plug and receptacle were turned over on their exteriorsides on a quantity of spherical solder balls so that a solder ballbecame embedded in each of the recesses. The solder balls used wereALPHAMETAL no flux 63SN/37PB spherical solder balls which had a diameterof 0.030 inch±0.001 inch and a weight of approximately 0.00195 g. Theplug and receptacle were then treated with FLUORAD, a solderanti-wicking material available from 3M Corporation. After suchtreatment the plug and receptacle were then dried in a convection ovenfor 2 hours at 105° C. The plug and receptacle were then positioned onseparate circuit boards made of conventional reinforced epoxy printedcircuit board material, having thicknesses of 0.061 inches. Referring toFIG. 9, a thermocouple was placed on the exterior surface of the plug inposition T. Another thermocouple was centrally positioned upon thesupporting board surface adjacent the plug. Both the plug and thereceptacle were then treated in a panel-infrared (IR) conveyer solderreflow oven. As is conventional for this type of oven, the plug andreceptacle were moved through six zones in the reflow oven. The conveyorspeed was 13 in/min. Heating temperatures in each zone are shown inTable 1. Minimum and maximum temperatures for the plug and for thesupporting board are shown in Table 2. Both positive and negativemaximum slopes are shown in Table 3. Rise time and fall time measured onthe board between 180° C. and 200° C. are shown in Table 4. Temperatureby time and distance for the plug is shown in the curve in FIG. 26 awherein the heavy line is the temperature at the thermocouple on thesupporting board and the light line is temperature at the thermocoupleon the plug exterior surface. A visual inspection of the plug and thereceptacle after solder reflow showed that nearly all the solder ballshad fused to the contact leads it their respective cavities. Solder ballheight above the exterior surfaces of the plug and the receptacle alsoappeared to be relatively uniform. There was no noticeable warping orbending of the housing.

Example 2

Another plug and receptacle were prepared in essentially the same way aswas described in Example 1 and solder balls were emplaced in therecesses on the exterior sides. Several hours after the treatment in thesolder reflow oven in Example 1, when atmospheric conditions weresomewhat different, another plug and receptacle essentially similar tothe ones used in Example 1 were subjected to similar reflow heating aswere used in Example 1, Oven conditions are shown in Table 1. Minimumand maximum temperatures of the plug and the adjacent supporting boardare shown in Table 2. Both positive and negative maximum slope is shownin Table 3, rise time and fail time measured on the board between 180°C. and 200° C. is shown in Table 4. Temperature by time and distance isshown in FIG. 26 b. It will be seen that the curve shown in FIG. 26 b issomewhat different than that shown in FIG. 26 a which difference isattributed to different ambient atmospheric conditions. A visualinspection of the resulting connector showed similar results to thoseachieved in Example 1.

TABLE 1 Temperature (° C.) Example ZONE #1 #2 #3 #4 #5 #6 1 UPPER 350Unheated 275 230 310 Unheated 1 LOWER Unheated Unheated 275 230 310Unheated 2 UPPER 350 Unheated 275 230 310 Unheated 2 Lower UnheatedUnheated 275 230 710 Unheated

TABLE 2 Connector Board Max Temp Time Max Temp Time Example (° C.) (Min.& Sec.) (° C.) (Min & Sec) 1 188 4:37.6 — — 1 — — 232 4:19.8 2 1914:53.2 — — 2 — — 229 5:10.4

TABLE 3 Positive and Negative Maximum Slope ° C. (Sec) Connector BoardTime Reached Time Reached Example Max (Min & Sec) Max (Min & Sec) 1 +20:50.4 +2 0:30.4 1 −2 6:45.2 −3 5:58.8 2 +3 7:08.0 +3 1:14.8 2 −156:13.8 −7 6:14.0

TABLE 4 Rise Time and Full Time Between 180° C. and 200° C. (Measured onBoard) Example Rise Time (Min & Sec) Fall Time (Min & Sec) 1 0:28.80:15.2 2 1:31.6 0:40.6

Example 3

Another connector was made using essentially the same conditions as weredescribed in Examples 1 and 2 except that the specific curves shown inFIGS. 26 a and 26 b may have been somewhat different because ofatmospheric conditions. After the completion of this connector, thesolder balls at six locations on the exterior surface of the plug wereexamined by Laser Point Range Sensor (PRS) available from Cyber OpticsCorporation of Minneapolis, Minn. Referring to FIG. 9, these locationsare identified as areas 27 a and 27 b when the laser was directed fromL₁, as areas 27 c and 27 d when the laser was directed from L₂ and asareas 27 e and 27 f when the laser was directed from L₃. At all theseareas a laser profile was taken of the profiles of the five solder ballsin each of these areas. Reproductions of these laser profile are shownin FIG. 27 a-27 f. The height of each of these solder balls at itshighest point above the plane of the exterior side of the plug is shownin Table 3. For each of these groups the solder ball closest to thefront of the plug as shown in FIG. 9 was considered the first positionin Table 5 and was the solder ball on the left of the graphs in FIGS. 27a-27 f. An examination of these results reveals that in each group offive solder balls there was what was considered to be an acceptabledegree of uniformity for the height of the solder balls.

TABLE 5 POSITION HEIGHT (.001 in.) GROUP 1 2 3 4 5 27a 18.1 18.9 19.519.6 19.1 27b 19.2 18.5 17.6 18.5 18.0 27c 20.4 21.1 21.6 21.1 21.4 27d19.9 20.1 20.1 21.2 20.5 27e 18.2 18.9 19.3 18.2 18.7 27f 19.1 18.2 19.018.2 18.9

Example 4

Another connector was made essentially according to the conditionsdescribed in Examples 1 and 2 except because of atmospheric conditionsthe specific curves shown on FIGS. 26 a and 26 b may have been somewhatdifferent. In almost all cases solder balls were satisfactorily fused tothe contact leads and solder balls were of an acceptably uniform heightabove the plane of the exterior surfaces of the plug and receptacle onvisual inspection. A stencil with a pattern matching the solder balls onboth the plug and receptacle was used to apply solder paste ontoconductive solder pads on two different circuit boards having athickness of 0.061 inches. The plug was positioned on one circuit boardand the receptacle was positioned on the other. The plug and receptaclewere then separately again treated in the conveyor oven under conditionssimilar to those described in fusing the solder balls to the contactsexcept that conveyor speed was decreased to 11 in/sec. After cooling,the plug and receptacle were found to have been satisfactorily fused totheir respective boards. A photograph showing these x-rays of selectedsolder balls are attached respectively at FIGS. 28 a and 28 b. Crosssectional electron microscope photographs were taken to show the fusingof the solder balls to the signal contact leads and the fusing of thesolder balls to the printed circuit board material. These electronmicroscope photographs are shown respectively at FIGS. 28 c and 28 d.There was only one short between adjacent signal contacts and goodconnections were made between the contacts and the solder balls andbetween the solder balls and the boards at all other points.

It will be appreciated that electrical connector and the method of itsmanufacture has been described in which the connector that can utilizeBGA technologies for mounting on a PWB. Surprisingly and unexpectedly itwas also found that there was a relatively high degree of uniformity inthe profiles of the solder balls and, in particular, in the weightsand/or volume of the solder balls.

While the present invention has been described in connection with thepreferred embodiments of the various figures, it is to be understoodthat other similar embodiments may be used or modifications andadditions may be made to the described embodiment for performing thesame function of the present invention without deviating therefrom.Further, the arrangements described can be used with respect tocomponents other than connectors, that comprise housings formed ofinsulative materials which carry elements to be fused onto a PWB orother electrical substrate.

Therefore, the present invention should not be limited to any singleembodiment, but rather construed in breadth and scope in accordance withthe recitation of the appended claims.

1-17. (canceled)
 18. An electrical connector comprising: an insulativehousing that defines an electrical contact passageway and an exteriorsurface adjacent to the electrical contact passageway; an electricalcontact on the insulative housing, wherein the electrical contactcomprises a free end and the electrical contact is inserted into theelectrical contact passageway of the insulative housing; and a body ofreflowable, electrically conductive material fused onto the free end ofthe electrical contact, wherein the electrical contact passagewaydefines an opening in the exterior surface of the insulative housing,the electrical contact is carried on the insulative housing by aninterference fit between a retention portion of the electrical contactand the housing, the body of reflowable, electrically conductivematerial does not extend into the electrical contact passageway, and theelectrical contact has a portion between the free end and the retentionportion that is spaced from wall that define the electrical contactpassageway.
 19. The electrical connector as claimed in claim 18 whereinthe body of reflowable, electrically conductive material is a solderball.
 20. The electrical connector as claimed in claim 18, wherein theelectrical contact has a medial portion and the medial portion has ananti-wicking material thereon